Monday, February 7, 2022

USB 5V 4A Car Charger using 78S05 with PCB

Fig. 1 - USB 5V 4A Car Charger using 78S05

This is a simple USB 5V 4A Car Charger circuit to charge a cell phone, tablet, or any other gadget that requires a voltage of 5V with a current of 2 Amperes via USB.

The circuit is a DC converter that takes power from a cigarette lighter socket in your vehicle, and converts the 12V battery voltage to a stabilized 5V voltage.

There are several models of USB chargers on the market, the problem is the high price, and the supply current is quite low, around 400mA to 600mA, smartphones currently have chargers with 1000mA, 1500mA, 2000mA... 

The circuit is based on the LM78S05 IC, it is extremely easy to build, using very few components. 

L78S00 Description

The L78S00 series of three-terminal positive regulators  is available in TO-220 and TO-3 package sand  with several  fixed output  voltages, making it useful in a wide range of applications. 

These regulators can provide local on card regulation, eliminating the distribution problems associated with single point regulation. Each type employs internal current limiting, thermal  shut-down and safe area protection, making it essentially indestructible. 

If adequate heat sinking is provided, they can deliver over 2A output current. Although designed primarily as fixed voltage regulators, these devices can be used with external components to obtain adjustable voltage sand currents.


  • Output Current to 2A.
  • Output  Voltage of: 5 ; 7.5 ; 9 ; 10 ; 12 ; 15 ;18 ; 24V.
  • Thermal Overload Protection.
  • Short Circuit Protection.
  • Output Transistor SOA Protection

Circuit Operation

In Figure 2, below, we can see the schematic diagram of USB 5V 4A Car Charger using 78S05, the Circuit's operation is pretty basic, what happens is that when you plug your USB converter into the cigarette socket of your car, it converts this 12V battery voltage to a regulated 5V voltage.

Fig. 2 - Schematic circuit USB 5V 4A Car Charger using 78S05

The total output current of the circuit is 4 Amps, 2A for each USB port, this is enough current to charge any USB device today.

The circuit has overload protection, which means that if there is a short circuit on the output, or if a device with higher current is connected to the USB converter, it will shut down, until that current is reduced to a maximum of 2A.

Components List

  • Semiconductors
    • U1, U2 ...... 78S05 Integrated Circuit Voltage regulator
    • LED1 ....  Light Emitter Diodo, general purpose

  • Resistor
    • R1 ..... 4.7KΩ (yellow, violet, orange, gold
    • RP1 ......... 10KΩ Trimpot
  • Capacitor
    • C1 .......... 47nF Ceramic Capacitor
    • C2 .......... 100nF Ceramic Capacitor
    • C3 .......... 4.700uF / 35V Electrolytic Capacitor 

  • Miscellaneous 
    • F1 .......... 20A - 250V soldering Fuse
    • P1 .......... 2-pin PCB soldering terminal blocks
    • P2 .......... 3-pin PCB soldering terminal blocks
    • Others .... Printed Circuit Board, heat sink, wires, etc.

Printed Circuit Board

In Figure 3, we provide the PCB - Printed Circuit Board, in GERBER, PDF and PNG files. These files are available for free download, on the MEGA server, in a direct link, without any bypass. 

All to make it easier for you to do a more optimized assembly, either at home, or with a company that prints the board. You can download the files in the Download option below.

Fig. 3 - PCB - USB 5V 4A Car Charger using 78S05

Files to Download, Direct Link:

Click on the link beside: GERBER, PDF and PNG files

If you have any questions, suggestions or corrections, please leave them in the comments and we will answer them soon.

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